1. Field of the Invention
The present invention relates to a light-emitting diode (LED) capable of being mounted on a motherboard of lighting devices, information terminal devices or the like, more specifically to an LED for illumination having, in particular, high brightness and excellent heat-dissipation properties.
2. Description of the Related Art
LEDs have been widely employed in various electrical devices as small electronic parts for illumination due to their long operational life, small size, high emission efficiency, low power consumption or the like.
LEDs can be easily solder-mounted on a surface of a motherboard of the devices by using a mounter and achieve an excellent mass-productivity of devices including LEDs, which are used, for example, illumination keys of mobile phones of small information terminal devices, light sources of lighting devices or light sources of liquid crystal backlights. LEDs with higher brightness, longer operational life and higher reliability are required.
One proposal for a conventional surface-mount LED is disclosed in Japanese Patent Application Publication No. 2000-216443 (see page 3 of the specification and FIG. 1). The proposed surface-mount LED includes a board made of a metallic thin plate, a reflection cup provided on the board and having an inverted conical recess, formed by a press process, an LED element disposed in the reflection cup, a first resin including a light collecting lens part disposed above the LED element and configured to seal the LED element, and a second resin configured to reinforce a back surface of the board.
With the above structure, because the LED element is placed on the board made of the metallic thin plate having a high heat-conducting efficiency, heat-generation of the LED element is transmitted through the board to a motherboard and dissipated thereon, thereby it is possible to curb the reduction of brightness of emitted light and increase a life span of the LED element.
A conventional LED as a light emitting device as disclosed in Japanese Patent Application Publication 2007-129053 (page 5, FIG. 3) has a structure including a base made of a material having a high heat conductivity and provided with a predetermined conductive pattern, a circuit board attached to the base and having an opening, an LED element die-bonded on the base at a position where the opening of the circuit board is disposed, upper electrodes provided on the LED element and wire-bonded to the predetermined pattern of the circuit board through gold wires, a case with a lens, attached to an outer circumferential edge portion of an upper surface of the circuit board to cover the LED element and having a sealing resin injection hole provided on an outer circumferential portion of the case, and a sealing resin formed by a resin injected from the sealing resin injection hole to cover the LED element. In the structure, because the base mounting the LED element is formed by an aluminum plate to which alumite treatment is applied, or a copper plate on which aluminum plating is applied, the structure has excellent corrosion resistance of a reflection surface, a high reflectance, and excellent heat-dissipation properties and is able to curb brightness deterioration due to heat because heat generation of the LED element is directly transmitted to the base.
However, in the conventional LED as disclosed in Japanese Patent Application No. 2000-216443, because the board is formed in a complicated shape including the reflection cup having a step, a conical recess and so on, from the metallic thin plate by way of the press forming, the board is easily deformed and lacks strength due to a characteristic of the press forming, and this gives rise to structural problems such as the need to reinforce the board made of the metallic thin plate by attaching a reinforced resin member to a back surface of the board or the like, thereby resulting in an increment in production costs due to an increased number of processes. In addition, because the board must be formed by a thin plate capable of being formed by the press, the board necessarily has a high heat resistance, and there is a problem with heat conductivity, possibly resulting in brightness deterioration.
On the other hand, in the conventional LED as disclosed in Japanese Patent Application Publication No. 2007-129053, because the LED element is disposed in the opening of the circuit board, light emitted from the LED element, especially, light emitted from a side surface of the LED element is almost all shielded by a wall of the opening of the circuit board. Consequently, there is a problem that the LED has a low light extraction efficiency. In addition, in the LED element, because the base is made of a metallic material such as aluminum or the like, electrodes cannot be formed directly on the metallic base and the electrodes (lower electrodes) used as mount-terminals when the LED is mounted on the motherboard by soldering cannot be formed on the base, and therefore, with such a structure, there is a problem that a surface-mount LED cannot be provided and therefore the use is very limited.